The present invention relates generally to a navigation system for an automotive vehicle. More specifically, the invention relates to a navigation system with a graphic display on which a road map, the instantaneous position of the vehicle, and a projected course are displayed. In more detail, the invention relates to a system and method for precisely detecting vehicle position and renewing or updating the vehicle position data for accurate navigation.
Recently, various vehicular navigation systems including graphic map displays on a display, such as a CRT monitor, have been proposed. In all such prior proposed navigation systems, it has been considered essential to monitor vehicle position and update the vehicle position data from time to time as the vehicle travels. Various sensors have been employed to detect the vehicle position.
A typical sensor for detecting vehicle position is the combination of a distance sensor which monitors distance travelled by the vehicle and a direction sensor for monitoring the direction of travel of the vehicle. However, with the sensors available nowadays, it is still difficult to precisely detect instantaneous vehicle position and there thus tends to be a certain amount of error. This error tends to accumulate as the distance covered by the vehicle increases. The accumulated error may become significant in cases where the travel distance is relatively long. Due to these accumulated errors, conventional navigation systems have not been adequately reliable for practical use.
On the other hand, when such vehicle position sensors are utilized to monitor relatively short travel distances the error in the resultant vehicle position data is rather small and can be disregarded. Therefore, over relatively short distances, the vehicle position sensors are practical for navigation. Therefore, if the initial position of the vehicle can be renewed or updated accurately at relatively short intervals of vehicle travel, precise navigation would be possible.
Furthermore, when a symbol representing vehicle position is superimposed on the road map displayed on the display monitor, the symbol tends to be misplaced due to errors in the distance sensor and/or the direction sensor signals. As such errors accumulate, the vehicle symbol on the display screen becomes farther and farther off course.